Numerical method for predicting IGE hover performance of a lifting rotor

To clarify influences induced by non-uniform ground surface on I.G.E. hover performance of a rotor, a numerical prediction method is developed by comb ining a foe-wake method with a panel method, where the most important featu re is the ability to determine blade flapping motions to be consistent with the deformed wake geometry. The ground surface beneath the rotor is substi tuted for quadratic panels with unknown ground vortex strength which are de termined by virtue of the non-penetration conditions at the collocation poi nts. The rotor blades are modeled by the lifting lines with a constant circ ulation which results in a wake structure to compose of deformed helical li ne vortices trailing from the blade tips. The numerical procedure is progra mmed as an interactive two-stage process, where the spatial arrangements of tip vortices are calculated at first by moving their nodal points with upd ated local velocities induced by the ground and trailing vortices and then proceed to the second stage where the equation of blade flapping motion is served using averaged induced velocity distribution on the rotor disc. Iter ations are executed until both the wake geometry and blade flapping motions are converged simultaneously. In this paper, we introduce typical numerica l results obtained for a rotor hovering in close proximity above a uniforml y inclined flat surface and discuss influences of the ground inclination an gle and rotor height on the wake geometry, flowfields around the rotor and the rotor-induced torque. The ground interaction effect on the amplitude an d phase angle of the blade flapping motion are also investigated, and their unique dependencies on the operating circumstances are clarified.